The present disclosure relates to a structure of a connecting rod of an engine, the connecting rod coupling a piston to a crankshaft.
When an engine is operating, its connecting rod is periodically subjected to various kinds of deformation such as expansion and contraction, bending, and twisting. It is known in the art that resonance caused by such deformations leads to noise and oscillations of the engine. To reduce oscillations, which occur at specific frequencies and cause such resonance, the known art proposes to install dynamic vibration absorbers, which oscillate in phases substantially opposite to those of the oscillations, at the connecting rod and its connecting portion.
Japanese Unexamined Patent Publication No. 2015-161322, for instance, discloses a connecting rod structure in which dynamic vibration absorbers are installed at two spots, namely the connecting rod and its connecting portion, to reduce oscillations of two specific frequencies. Specifically, in order to reduce resonance occurring at 3.3 kHz when the connecting rod expands and contracts, a first dynamic vibration absorber is installed inside a piston pin which is coupled to a smaller end part of the connecting rod. In addition, in order to reduce resonance which occurs at a frequency of 1 to 2 kHz and may be noticeable next after having reduced the resonance caused by the expansion and contraction of the connecting rod, a second dynamic vibration absorber is installed at a larger end part of the connecting rod which is coupled to a crankshaft.
In the connecting rod structure disclosed in Japanese Unexamined Patent Publication No. 2015-161322, dynamic vibration absorbers which handle specific frequencies are installed. Thus, while resonances occurring at the designated frequencies can be reduced with a high degree of precision, it is necessary to install a dynamic vibration absorber for each frequency. Therefore, further dynamic vibration absorbers, such as third and fourth dynamic vibration absorbers, need to be installed in order to reduce resonance occurring over a wide frequency band. As an inevitable result, the connecting rod and its connecting portion are designed in a more complex manner and the structure is increased in weight. Moreover, since the number of dynamic vibration absorbers which can be installed is limited, the frequency band at which resonance can be reduced is also limited.
In view of the foregoing, the present disclosure attempts to provide a connecting rod which allows for reducing resonance occurring over a wide frequency band while having a simple structure which hardly increases the weight of the connecting rod.
The art disclosed relates to a connecting rod coupled to a reciprocating piston and to a rotating crankshaft inside an engine.
The connecting rod includes: a rod having the form of a bar; a smaller end part provided at one end of the rod and coupled via a piston pin to the piston in a rotatable manner; and a larger end part provided at an other end of the rod and coupled via a crank pin to the crankshaft in a rotatable manner. The rod is provided with a friction generation portion at which friction is generated due to deformation of the rod.
That is, in this connecting rod, the rod is provided with a friction generation portion at which friction is generated due to deformation of the rod. When the rod deforms, frictional heat is thus generated at the friction generation portion due to the friction. As a result, energy acting on the rod declines, which is why oscillation of the rod can be reduced. As long as friction is generated, various kinds of deformation, such as expansion and contraction, bending, or twisting, can be handled and oscillation over a wide frequency band can be reduced. Since it is sufficient to just provide the friction generation portion, there is no need for a complicated structure and the weight of the connecting rod is hardly increased. In addition, in comparison to the case where—as disclosed in the known art—a dynamic vibration absorber is installed inside the piston pin, the structure in which the rod is provided with a damping element comprising the friction generation portion has the effect that reciprocating weight when the piston is reciprocating can be reduced.
Specifically, the connecting rod further includes a damping element at least attached to the rod, wherein the friction generation portion is provided by at least partly pressing the damping element and the rod together.
The friction generation portion may be provided by processing the connecting rod itself. Alternatively, however, the friction generation portion can be provided in an easier manner by attaching such a damping element to the connecting rod.
More specifically, the damping element is attached to the connecting rod by a first fixed portion and a second fixed portion which are spaced apart from each other. The first fixed portion and the second fixed portion have different mounting strengths. At least one of the first fixed portion and the second fixed portion is capable of friction.
Thanks to this configuration, friction of different friction force can be obtained over a wide area of the rod. Therefore, oscillation over a wider frequency band can be reduced.
In this case it is in particular beneficial if the first fixed portion which is capable of friction and has a low mounting strength is arranged near the smaller end part, and if the second fixed portion which has a high mounting strength is arranged near the larger end part.
According to this configuration, the friction generation portion can be provided near the smaller end part which has a relatively high deformation rate. Therefore, oscillation can be reduced even more effectively as high frictional heat is generated.
Further, the damping element may be a flat element extending in a curved manner along the rod, both end portions of the damping element being attached to the rod and an intermediate portion of the damping element being pressed onto the rod.
In this case, the intermediate portion of the damping element is pressed to the rod while being in surface-to-surface contact with the rod over a wide area. Therefore, a friction generation portion capable of friction can be provided at the intermediate portion of the rod.
Furthermore, the damping element may be a flat element extending in a curved manner along the rod, an intermediate portion of the damping element being attached to the rod and both end portions of the damping element being pressed onto the rod.
In this case, the end portions of the damping element are pressed onto the rod, and friction generation portions capable of friction can be provided at both end portions of the rod.
Moreover, the damping element may be press-fitted into a slot formed inside the rod.
In this case, the damping element is pressed onto an inner peripheral surface of the slot. Therefore, the rod can be provided with a friction generation portion capable of friction.
The connecting rod disclosed herein allows for reducing resonance occurring over a wide frequency band while having a simple structure which hardly affects the weight of the connecting rod.